A cartridge-type fountain pen of the above described general type is described in German Patent Document DE-AS 24 41 610. This pen has the advantage that, apart from having a conventional ink writing element, e.g. a writing tip or nib, it can be provided at the opposite end with an applicator, for example, a capillary body, fiber tip, ball, tube or the like, from which another medium can be applied to the substrate (e.g. a paper sheet). For example, the reservoir or container for this other medium may form part of a correction system enabling a correcting liquid to be applied to the paper. A correcting liquid can be, for example, an agent which is capable of removing the color of previously applied ink, i.e. a bleaching substance, a substance capable of transforming the dyestuff of an ink into a colorless substance, or some other so-called "ink eradicator".
In general, when the ink eradicator liquid is to be dispensed from the second reservoir, it is provided with a fiber or felt tip as an applicator.
Of course, in place of the ink eradicator reservoir, a reserve cartridge with writing ink can be accommodated in the reserve space if this is desired. The reserve space and the reservoir, as a result, generally have shapes which are intended to match the configuration of the ink cartridge used for the fountain pen so that both the eradicator-liquid reservoir and a reserve cartridge can be interchangeably and selectively received in the reserve compartment.
With this conventional fountain pen, however, it has been found to be disadvantageous that the second cap is applied to a neck-shaped portion of the eradicator fluid reservoir so as to be held directly by the latter. This means that a relatively small diameter portion serves to hold the cap and limits the dimensions and shape of the applicator element for the eradicator liquid.
When, in place of the correction liquid reservoir, a reserve ink cartridge is provided in the reserve compartment, the open end of the housing or barrel is not closed and the appearance of the fountain pen is detrimentally affected.
Furthermore, in this system, the end of the ink cartridge which must communicate with the nib during later use tends to become contaminated and there is a danger that the coupling end of the reserve ink cartridge will become so soiled that it cannot be properly received in the nib portion of the fountain pen.
Finally, there is a danger that contamination of this end of the reserve ink cartridge may result in leaking of the ink during use or that leakage may occur because of damage to the coupling end of the cartridge.
The fountain pen described in German Patent Document 36 42 283 has a replaceable ink eradicator part located at the end of the fountain pen barrel opposite that provided with the writing tip. The ink eradicator cartridge in this case has a tip which can receive a sealing cap which is form fittingly and friction fittingly received on this tip.
The sealing cap and the eradicator cartridge end of the tip are formed respectively with identical outer screw threads and the open end of the barrel housing and an end cap cooperating therewith have respective inner threads cooperating with the outer threads. In this construction, the tip and the sealing cap can be screwed into the barrel housing or the end cap so that the end cap is connected with the barrel by this ink eradicator unit.
In this construction, the applicator region can have a larger diameter and enables closure of the housing or barrel by an end cap.
However, the requirement for numerous screw threads makes the system expensive and, in addition, this system cannot accommodate a reserve ink cartridge.
German Patent 35 38 077, corresponding to U.S. Pat. No. 4,759,651, describes a cap for the writing tip of a fountain pen which comprises a sleeve adapted to be pressed over the barrel and in which a sealing unit is provided for the writing tip.
In the region of the writing tip, this fountain pen comprises an annular bulge with which the inner bore of the sealing unit can come into sealing engagement.
A second annular bulge serves for fastening the sleeve on the barrel.
Upon application of the cap to the writing end of the instrument, the sealing member is shifted into the sleeve as the latter is placed upon the barrel, thereby enabling the first bulge to be pressed into the sealing unit and thereafter enabling the sleeve to engage the second bulge. In this writing instrument the sealing unit also serves as a signal element which can project beyond the opposite end of the sleeve from that having the opening receiving the barrel, to indicate the fact that the cap has been properly seated on the tip.